Field of the Invention
The present invention relates to an angular inertial sensor such as rate gyros or free gyros.
Brief Discussion of the Related Art
Such an inertial sensor comprises a support structure and seismic bodies (also known as seismic masses or test masses) that are generally arranged side by side and connected to the support structure by resilient hinges in order to be movable in a suspension plane defined by two orthogonal directions of movement for the seismic bodies. The elasticity of the hinges associated with the masses of the seismic bodies defines the frequencies of the resonant modes of the seismic bodies.
The resonator constituted by the seismic bodies and by the resilient hinges possesses two working modes of vibration, defining two directions of movement of the seismic bodies. Detecting vibration of the seismic bodies in these directions enables an angle to be measured.
The sensor also has actuators arranged to set the seismic bodies into vibration and detectors arranged to detect the relative movements of the seismic bodies. The detectors generally comprise pairs of electrodes, one of which is secured to one of the seismic bodies and the other of which is secured to the support structure. This makes it possible to detect the movements of the seismic bodies and then, by processing, to determine the movements of the seismic bodies relative to each other. Nevertheless, the measurements include components that are associated with parasitic movements between the seismic bodies and the support structure due to other resonant modes of the seismic bodies, which components can be particularly damaging for the performance of the sensor when the detectors have gains that are different.
Requirements concerning the detection of attitude and speed, e.g. for the purposes of piloting a vehicle or of navigation, require the performance of such sensors to be improved.
Various solutions have been proposed, such as for example in Document FR-A-2 983 574.